1. Technical Field
The present invention relates to an oscillator, an electronic apparatus, and a moving object.
2. Related Art
JP-A-1-82809 discloses that in a digitally temperature compensated crystal oscillator, a circuit configuration can be simplified by generating a temperature compensated voltage with an R-2R type D/A converter.
In the digitally controlled oscillator whose oscillation frequency is controlled by a control signal that is obtained by subjecting a digital signal to D/A conversion as disclosed in JP-A-1-82809, noise that is generated when a changeover switch included in an R-2R type resistor ladder is switched in response to the digital signal is a problem. Since the changeover switch is disposed on a current path from a reference voltage, a current that flows into a resistor group rapidly changes at the time of switching the changeover switch. Therefore, the noise is difficult to reject by a regulator or a small-capacity capacitor, and flows out to a common power supply with an oscillation circuit, causing a problem of degrading noise characteristics of an oscillator output. Moreover, D/A converters, such as those of the resistor ladder type other than the R-2R type, the pulse-width modulation (PWM) type, the delta-sigma type, and the capacitor array type, suffer from a similar problem.
Noise that is superimposed on a control signal can be reduced by a low-pass filter or the like. However, in order to sufficiently reduce noise that is generated in a power supply, a large capacitor or the like has to be mounted, which may fail to meet the need for miniaturization of an oscillator. Especially when a high-resolution digitally controlled oscillator with a digital signal of 12 bits or more is realized, the noise generated due to a rapid change in the current flowing into the resistor group at the time of switching of the changeover switch is a serious problem.